Add descriptions to the functions in quantum.h
Added squeeze() to eliminate singleton dimensions from tensors.
Added sparse_1d_hamiltonian() to easily create matrices for 1D problems.
Added sparse_1d_Hamiltonian(...) over vectors of tensors, fixing the declaration of the simplest variants.
Added missing declarations for sparse_1d_hamiltonian()
Added the base class Hamiltonian
Added tranlationally invariant Hamiltonians
Added ConstantHamiltonian and implemented the duplicate() method in those structures.
Commented the Hamiltonian classes.
Added decompose_operator()